Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mouse saliva contains a potent inhibitor of complement activity. The secretion of this inhibitor appears to be regulated by action on alpha-adrenergic receptors for two reasons. First, an alpha-agonist (norepinephrine) elicited saliva with a 260-fold higher specific activity of the inhibitor than that obtained with a cholinergic agent (pilocarpine). Second, the alpha-agonist elicited saliva having 43-foldgreater specific activity than that obtained following administration of a beta-adrenergic agonist (isoproterenol). This anticomplementary factor probably proteolytically degrades one or more of the complement components since it is inhibited by several protease inhibitors. The salivary anticomplementary factor is more potent than trypsin, chymotrypsin, thrombin, or Kallikrein. The anticomplementary factor has a pattern of inhibition like that of Kallikrein but unlike those of trypsin or chymotrypsin.
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PMID:Alpha-adrenergic regulation of the secretion of an anticomplementary factor in mouse saliva. 126 87

Blood proteins could play a critical role in the pathogenesis of cerebral vasospasm in subarachnoid hemorrhage (SAH) as agonists and as antagonists of vasoconstriction. The present study was designed primarily to quantify the inhibition produced by antithrombin III of the phasic responses elicited by cumulative doses of KCl, serotonin (5-HT), uridine triphosphate (UTP), and thrombin in isolated canine basilar arteries, and to ascertain whether other proteins might act similarly. Antithrombin III (1 unit/ml and 3 units/ml) given 2 min beforehand inhibited all agonists. The inhibition was not dependent on a functional endothelium nor due to stimulation of the electrogenic sodium pump. Alpha2-macroglobulin (0.1 mg/ml and 0.4 mg/ml) inhibited the contractile responses to high K+, 5-HT and thrombin. Kallikrein (1 and 4 units/ml) did not inhibit UTP but inhibited high K+ and 5-HT through an effect on the endothelium. Kallikrein (1 unit/ml) irreversibly blocked the responses to thrombin. Globulins (3 mg/ml) and fibrinogen (0.3 mg/ml) were not inhibitory. The results demonstrate that anticoagulant proteins are very effective nonspecific inhibitors of the vasoconstriction, whereas the serine protease kallikrein selectively blocks thrombin. The remarkable potency of antithrombin III suggests that it may protect cerebral arteries from exhibiting vasospasm in SAH.
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PMID:Vasodilator proteins: role in delayed cerebral vasospasm. 242 60

High molecular weight kininogen (HMWK) functions as a cofactor for activation of plasma serine zymogens and as an inhibitor of tissue cysteine proteases. Cell surfaces to which HMWK binds may provide sites for regulation of these systems. Localization of these HMWK-dependent processes at sites of vascular injury may depend on its binding to specific receptors on endothelial cells. In culture, passaged human umbilical vein endothelial cells (HUVEC) bind anti-HMWK antibody to the cell surface and contain 171 +/- 75 ng of HMWK/10(8) cells. [35S]Methionine-labeled HUVEC in culture synthesize a 120-kDa protein immunoisolated using an anti-kininogen antibody, and a 3500-nucleotide message for human HMWK was detected by Northern blot in RNA extracted from HUVEC. HUVEC also express unoccupied binding sites for HMWK on their surface. 125I-HMWK specifically binds to HUVEC in a reaction requiring Zn2+. 125I-HMWK binding to HUVEC is saturable at 4 degrees C but not at 23 degrees C. 125I-HMWK binds to HUVEC with equal affinity as unlabeled HMWK. Kallikrein, factor XII, fibrinogen, fibronectin, and thrombin do not inhibit 125I-HMWK binding to HUVEC. 125I-HMWK-HUVEC binding remains fully reversible at 60 min following the addition of a 50-fold molar excess HMWK. HUVEC express 9.3 +/- 2.0 X 10(5) (mean +/- S.E.) HMWK binding sites/cell (Kd = 52 +/- 13 nM). Both added and cell-bound 125I-HMWK migrate at 120 kDa on sodium dodecyl sulfate gel electrophoresis, suggesting that the protein remains uncleaved upon binding to the HUVEC surface. These studies indicate that HUVEC synthesize HMWK and the HUVEC surface has a site for its expression. By synthesizing and localizing HMWK to the cell surface, endothelial cells may contribute to the activation of plasma's contact serine zymogens and regulation of tissue cysteine proteases.
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PMID:The expression of high molecular weight kininogen on human umbilical vein endothelial cells. 246 Apr 46

Human factor IX circulates as a single-chain glycoprotein. Upon activation in vitro, it is cleaved into disulfide-linked light and heavy chains and an activation peptide. After reduction of activated 125I-factor IX, the heavy and light chains are readily identified by gel electrophoresis. A direct, immunoradiometric assay for factor IXa was developed to assess activation of factor IX for proteases that cleaved it. The assay utilized radiolabeled antithrombin III with heparin to identify the active site and antibodies to distinguish factor IX. After cleavage of factor IX by factor XIa, factor VIIa-tissue thromboplastin complex, or the factor X-activating enzyme from Russell's viper venom, antithrombin III bound readily to factor IXa. Cleavage of 125I-factor IX by trypsin, chymotrypsin, and granulocyte elastase in the presence of calcium yielded major polypeptide fragments of the sizes of the factor XIa-generated light and heavy chains. Kallikrein did not cleave the zymogen. Nonactivation cleavage was noted by thrombin, but only in the absence of calcium. When the immunoradiometric assay was used to assess trypsin-cleaved factor IX, the product bound antithrombin III, but not maximally. After digesting with insolubilized trypsin, clotting activity confirmed activation. In contrast, incubation of factor IX with elastase (Takaki A et al, J Clin Invest 71:1706, 1983) or chymotrypsin did not lead to generation of an antithrombin III-binding site, despite their digestion of 125I-factor IX into heavy and light chain-sized fragments. In evaluating activation of factor IX, physical evidence of activation cleavages does not necessarily correlate with generation of an active site.
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PMID:Cleavage and activation of human factor IX by serine proteases. 638 97

A protein extract was obtained from normal human serum by adsorption to unsubstituted Sepharose 4B. This extract contained one or several enzymes with SAA and AA degrading capacity. The optimal pH for degradation of SAA was about 7.3. On fractionation of the enzyme extract on Sephadex G-160, the active component was eluted in the V0 peak. The V0 fraction, which on double immunodiffusion analysis was found to contain alpha 2-macroglobulin, was also active against synthetic substrates used to determine the activity of thrombin and plasma kallikrein. Gel filtration under dissociating conditions and molecular weight estimation further indicated the presence of those enzymes in the preparation. Several serine proteases which are known to be inhibited by alpha 2-macroglobulin possessed AA and SAA degrading activity. On degradation of SAA, an intermediate split product with molecular weight similar to AA was formed. Kallikrein, plasmin and elastase were also able to degrade intact amyloid fibrils suspended in phosphate-buffered saline.
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PMID:Degradation of amyloid proteins by different serine proteases. 646 Oct 61

A study was made of the interaction between prothrombin and enzymes: blood plasma kallikrein and factors alpha-XIIa and beta-XIIa immobilized on enzacryl-AH. Kallikrein-induced prothrombin proteolysis was accompanied by a decrease in prothrombin activity, appearance of BAME-esterase and poor clotting activity. As a result of fractionation of products on the column with DEAE-Sephadex A-50, some fractions that have thrombin amidase activity (splitting of the substrate S-2238) and high antithrombin activity were obtained. Antithrombin activity manifested in the inhibition of fibrinmonomer aggregation during fibrin formation. During incubation with prothrombin, factors alpha-XIIa and beta-XIIa also stimulated the appearance of BAME-esterase activity. None of the immobilized enzymes activated factor X.
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PMID:[Prothrombin--substrate for blood plasma kallikrein and factor XIIa]. 660 74

Exposure of human blood polymorphonuclear leukocytes (PMN) to purified active plasma kallikrein resulted in PMN aggregation when kallikrein was present at concentrations ranging from 0.4 to 0.6 U/ml (0.18-0.27 microM). Kallikrein-induced PMN aggregation was not mediated through C5-derived peptides, because identical responses were observed whether or not kallikrein had been preincubated with an antibody to C5. Moreover, kallikrein was specific for aggregating PMN, because no aggregation was observed with Factor XII active fragments (23 nM), Factor XIa (0.6 U/ml or 15nM), thrombin (1.6 microM), plasmin (2 microM), porcine pancreatic elastase (2 microM), bovine pancreatic chymotrypsin (2 microM), or bradykinin (1 microM). Bovine pancreatic trypsin (2 microM) aggregated PMN, but to a lesser extent than kallikrein (0.18 microM). Kallikrein was a potent aggregant agent for PMN because similar responses were observed with kallikrein (0.5 U/ml or 0.23 microM) and an optimal dose (0.2 microM) of N-formyl-methionyl-leucyl-phenylalanine. In addition, PMN incubation with kallikrein resulted in stimulation of their oxidative metabolism as assessed by an increased oxygen uptake. Neutropenia and leukostasis observed in diseases associated with activation of the contact phase system may be the result of PMN aggregation by plasma kallikrein.
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PMID:Purified human plasma kallikrein aggregates human blood neutrophils. 691 55

Prekallikrein was purified from guinea-pig plasma. The prekallikrein appeared homogeneous as a single-chain protein on polyacrylamide gels in the presence of sodium dodecyl sulfate (SDS) and beta-mercaptoethanol. The apparent molecular weight was 82 000 by SDS-polyacrylamide gel electrophoresis, 99 000 by gel filtration on a Sephadex G-150 column and 84 500 (protein part) by amino acid analysis. The isoelectric point was approx. 9.0. The purification method yielded 3.8 mg (A280 3.800) of prekallikrein from 500 ml of plasma. Kallikrein was generated from the prekallikrein by limited proteolytic action of a prekallikrein activator which was derived from guinea-pig skin. From analysis using SDS-polyacrylamide gel electrophoresis, the kallikrein has two fragments with apparent molecular weights of 52 000 and 40 000 which are linked by disulfide bond(s). The 40 000 molecular weight fragment was shown to incorporate [3H]diisopropylfluorophosphate. The kallikrein hydrolyzed the synthetic substrates containing the Phe-Arg sequence at the COOH-terminal, and it cleaved carbobenzyloxy-Phe-Arg-4-methylcoumaryl-7-amide more readily than Pro-Phe-Arg-methylcoumaryl-7-amide. The Km for the kallikrein with carbobenzyloxy-Phe-Arg-methylcoumaryl amide was 2 times 104 M. Also, the kallikrein showed negligible activities on peptide-methylcoumaryl amide-substrate for alpha-thrombin, Factor Xa or plasmin.
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PMID:Purification of guinea-pig plasma prekallikrein. Activation by prekallikrein activator derived from guinea-pig skin. 696 37

Cardiopulmonary bypass causes hemorrhagic complications, and initiates a chemical and cellular inflammatory response. Contact of blood with synthetic surfaces leads to qualitative and quantitative alterations in platelets, neutrophils, complement, and contact systems. Despite the fact that cardiopulmonary bypass is carried out in the presence of high doses of heparin, there is significant activation of both platelets and neutrophils. Thrombin is protected on cell and fibrin surfaces from antithrombin, even in the presence of high doses of heparin (approximately 5 U/ml). We therefore studied the effect of a small (Mr = 497), highly effective (Ki = 41 pM), reversible tripeptide inhibitor of thrombin, DUP 714 (1 microM), in a well characterized model of simulated extracorporeal circulation. In the absence of DUP 714, platelet counts decreased by 75% 5 min after the start of extracorporeal bypass and increased to 48% at 120 min of recirculation. DUP 714 significantly preserved platelet counts, decreased plasma levels of platelet beta-thromboglobulin levels, but did not prevent a decrease in sensitivity of platelets to adenosine diphosphate. Kallikrein-C1-inhibitor and C1-C1-inhibitor complexes increased progressively from 0.32 U/ml to 0.67 U/ml and from 4.45 U/ml to 7.25 U/ml, respectively, during 120 min of recirculation without DUP 714. Addition of DUP 714 significantly inhibited kallikrein-C1-inhibitor complex formation but did not affect C1-C1-inhibitor complexes. In the absence of DUP 714, human neutrophil elastase levels rose from a baseline of 0.01 +/- 0.00 microg/ml to 1.18 +/- 0.21 microg/ml during 120 min of recirculation. Human neutrophil elastase release at 120 min was significantly inhibited in the presence of DUP 714 to 37% of the value with heparin alone. These results indicated that addition of this novel thrombin (and kallikrein) inhibitor to heparin preserved platelet counts, decreased platelet secretion, and provided the additional benefit of partially blocking neutrophil activation during simulated extracorporeal circulation.
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PMID:Thrombin and human plasma kallikrein inhibition during simulated extracorporeal circulation block platelet and neutrophil activation. 979 91

A new hypothesis for activation of the contact system of plasma proteolysis (i.e., the plasma kallikrein/kinin system) is presented. Kininogens have a multiprotein receptor on endothelial cells which consists of at least cytokeratin 1, urokinase plasminogen activator receptor, and gC1qR. When contact proteins (high molecular weight kininogen followed by prekallikrein) assemble on the kininogen receptor on endothelial cells, an endothelial cell membrane cysteine protease is expressed to activate prekallikrein to kallikrein. On endothelial cells, prekallikrein activation is independent of factor XIIa activation. Activation of prekallikrein on endothelial cells results in kallikrein cleaving its receptor high molecular weight kininogen to liberate bradykinin. Bradykinin liberation stimulates release of tissue-type plasminogen activator from endothelial cells. Kallikrein formation also results in kinetically favorable pro-urokinase activation on endothelial cells with subsequent plasminogen activation. In addition to stimulating cellular fibrinolysis, kininogens contribute to the constitutive anticoagulant nature of the intravascular compartment. Kininogens block calpain's participation in forming the heterodimeric complex of platelet integrin alpha IIb beta 3. Kininogens also block thrombin from binding to the thrombin receptor(s) on platelets. Last, kininogens prevent thrombin from cleaving protease activated receptor 1 after arginine41. These combined data indicate a biologic system for activation of the plasma kallikrein/kinin system and physiologic consequences as result of this activation.
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PMID:Plasma contact activation: a revised hypothesis. 983 May 13


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